Method of making steel



Patented Nov. 25, 1941 UNITED STATES PATENT OFFICE METHOD OF MAKINGSTEEL Albert E. Greene, Seattle, Wash.

No Drawing. Application December 11, 1937,

' Serial No. 179,333

2 Claims.

This invention relates to improvements in the method of making steel ofimproved physical properties, and more particularly to an improvedmethod of securing improved physical properties such as yield strengthand ductility, and testing the molten steel prior to pouring or tappingit from the furnace.

I found, in the course of certain electric ,steel melting operations,that by taking spoon samples from the bath from time to time after thebath was melted and pouring these spoon samples. into test bars,theimprovement in physical properties could be readily checked. I hadnever before taken spoon samples of the bath prior to the alloydeoxidizing additions and pulled test bars made from these spoon samplesfrom the bath while the bath was held in the furnace. I found that spoonsamples from the bath could be poured into testbars which could bepulled to ascertain tensile properties, both strength and yield point ofsample test bars increased during the treatment given the steel in thefurnace, and these test bars were pulled in the as-cast andun-heattreated condition. These test bars were cast in green sand moldsclose to a diameter-of .505". The test bars had enlarged ends forholding by the grips of the'testing machine. An example of the resultsis as follows. A steel heat containing about .30% carbon and .30%manganese and not over 40% silicon, all residual except possibly a smallamount of carbon, that is, without any alloy additions, showedincreasing tensile results in the as-cast, un-heat-treated test bars,from about 50,000 psi at the start of taking samples to a tensilestrength of 80,000 at the finish of the heat. Other heats ofthis sameapproximate composition showed tensile strength as high as 100,000 psi.Furthermore, the yield strength at the end of the heat was between50,000 and 65,000 psi for these heats, and the ductility was excellentas measured by the improvement of grain and fracture appearance as wellas in elongation and reduction of area. In the steel with the bestphysical tensile and yield strength for a carbon content under about.40% the fracture of the pulled and broken specimens was silky, that isfor the fully reduced steels. This silky fracture in such as-cast testbars is new, as far as I am aware.

I have never seen itin an un-heat-treated test bar of any suchcomposition, or even with much higher alloy contents. a I have foundthat the test bars made from the upper level or strata of the steel bathunder the reducing slag will show the silky fracture and othercorrespondingly improved physical properties, whereas a test bar madefrom the steel farther down in a deep bath, which steel is notsufficiently reduced, will not show the silky fracture or correspondinghigh tensile properties.

My improved method of this application is intended to ascertain andcheck the quality of the steel during and after the deoxidizing orreducing treatment to which it is subjected. The tests which showed theimproved physical properties were taken from the bath of steel after ithad been sufliciently treated or deoxidized. These improved physicaltest results were obtained in steel made in electric arc furnaces wherethe temperature of the bath was maintained only slightly abovethemelting temperature, that is enough so;

that spoon samples of the molten steel could be readily taken and pouredfrom the spoon, and where the slag composition was controlled and wherethe bath was subjected to reducing action of added reducing agents.

An example of the method of this invention will now be given. In thecase of a heat of high strength steel I may use either an acid hearthelectric furnace or a basic hearth electric furnace. Using an acidhearth, a scrap charge is selected which is sufliciently low inphosphorus and sulphur to not require removal of either, and the contentof carbon is preferably below that which is desired in the finishedsteel, for example under .30 percent carbon. This scrap charge is put inthe furnace on the hearth. Sand and limestone to make slag are alsocharged, in suificient quantities to give a covering slag preferably atleast a half inch thick. The proportions of sand and limestone may beabout equal and the slag, after physical strength. If this is the casethe reduc-v The first test bar thus made ing action on the steel iscontinued. This reducing action can be accomplished by throwing on theslag covering a fine carbon reducing agent or some other reducing agent,in particulansilicon. However, without any silicon addition, and withoutany other alloy additions, continuance of the reducing treatment on theslag bath will result in the improved physical properties, if carriedout as above described, that is, at the relatively low molten bathtemperatures. Then, when the steel is sufl'iciently reduced, the tensiletest bars will show the improved properties already described, andfurthermore, these improved results are found to occur in the test barsas-cast and pulled without heat treatment. Thus, this invention providesa means for making the steel and having assurance that it is in the highstrength condition before it ever leaves the furnace. When the steel isin the improved condition, the as-cast and un-heat-treated test bar willshow the silky fracture in the pulled apart specimen containing carbonnot over about .40 per cent.

The operation can be carried out in a basic furnace as well as one withan acid (silica) hearth. In the basic furnace the slag will preferablybe on the basic side, that is, it may be made of sand and lime orlimestone, but the silica in the basic slag is preferably kept down tobe- .tween 25 and per cent of the total silica andlime content of theslag, that is a slag containing about 18102 to 2Ca0.

What I claim is:

1. In the production of steel and iron, the

method of determining the quality of the metal tensile machine whileholding the molten steel in the furnace, and continuing the treatment inthe furnace until the desired tensile or yield strength is attained in asample tensile specimen.

ALBERT E. GREENE.

